Selective Quench-Labeling of the Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene in the Presence of Trialkyl-Aluminum Chain-Transfer Reagents

Abstract

The pyrenyl-isonitrile quench-labeling reagent selectively labels Hf-polymeryls over Al-alkyl species allowing for quantification of active site counts in polymerization. This selectivity also enables differentiation between catalyst-bound and Al-bound polymer molecular weight distributions (MWDs) via dual detection gel permeation chromatography (GPC) methods (UV-GPC and RI-GPC) in the Hf-pyridyl amidocatalyzed polymerization of 1-octene. Inhibition of polymerization is observed when using trialkyl aluminum chain-transfer agents with this catalyst system; for AlEt 3 , such inhibition can be eliminated by addition of the chain-transfer reagent after initiation of polymerization. Inhibition of polymerization cannot be eliminated when AlMe 3 is used in these polymerizations. With Al i Bu 3 , a larger ß-branched Al-alkyl, polymerization is not inhibited. For AlEt 3 , the propagation to exchange coefficient (k ex /k p ) was determined; compared with ZnEt 2 , chain transfer is approximately an order of magnitude slower. Through I 2 labeling and NMR analysis of polymer chain ends, the concentration of Al-polymeryls is quantified.

Quantification of active sites in single-site group 4 metal olefin polymerization catalysis

“…Hence, compared to AlEt3, AlMe3 is likely to affect both the initiation and the propagation phases. Noteworthy, when AliBu3 was used under the same conditions, neither the polymerization nor the formation of active sites was altered [84].…”

“…This method provides also the "live" evolution of MWD at the different times of quench-labelling.Most importantly, the method proved selective towards Hf-polymeryl[82][83][84] species in the presence of ZnMe2 and ZnEt2 as chain-transfer agents upon using the isocyanato-pyrene as the quench reagent[83]. In a similar way, a selective count of Hf-polymeryl species in the presence of trisalkylaluminum compounds was achieved with the nitrile-pyrene as the quench reagent[84] (although it was ineffective with the rac-{EBI}ZrMe2/B(C6F5)3 system; vide supra).This quench-labelling method was used for studying 1-octene polymerization with a Dow's hafnium pyridine-amidinate catalyst; it returned quite variable fractions of active sites in the range 3-70%, depending on the conditions, especially the nature of the activator[82] (see 4.3).Yet, to our knowledge, the method has not been evaluated using MAO as co-activator.Quench-labelling with O 2Cipullo and Busico reported a simple method for quench-labelling of Zr-polymeryl chains with pure O2 yielding, after an acidic work up, macromolecules capped with single hydroxyl groups[85] (Scheme 10). Yet, the O2 quench-labelling efficiency was about 80%; the remaining 20% of propagating species are quenched by the acidic work-up, affording saturated chain-ends.…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In other catalysis [performed with Pd complexes constructed via N-heterocyclic carbene (NHC) ligands], the influence of substituents at the 2,6-position in aryl-N moieties is substantial, and derivatization of the NHC ligand has been carried out by replacing common 2,6-diisopropylphenyl-N parts with 2,6-di(3-pentyl)phenyl-N and 2,6-di(3-heptyl)phenyl-N moieties [30,31]. Much research has also been performed on I [32][33][34][35][36][37][38], and the synthesis of its analogs with the aim to improve the catalytic performance deserves attention [7,29,[39][40][41][42]. Subtle change in the ligand framework sometimes results in dramatic improvement in the polymerization performance and, hence, modification of the substituents has been a main research theme in the development of postmetallocecenes [43][44][45][46][47][48][49].…”

Ethylene-co-norbornene Copolymerization Using a Dual Catalyst System in the Presence of a Chain Transfer Agent

“…This is probably due to the difficulties in finding a good combination of catalysts and chain shuttling agents. Interest in understanding polymerization mechanism of this catalysis [19,20,21] and properties of polymers obtained by this technology [22,23,24] is revealed by recent excellent studies. Seldom one of the catalysts is an ansa -metallocene.…”

“…Ethylene and norbornene copolymers, poly(E- co -N)s, are one class of polymers made possible by the discovery of metallocene catalysis [25,26,27,28,29,30,31]. Random poly(E- co -N)s with norbornene content above 20 mol % are amorphous materials with an exceptional combination of properties [16,17,18,19,20,21,22]. They are materials of high commercial interest used in optics, capacitor films, medical and diagnostic applications food and drug packaging.…”